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Species: Silver sagebrush is widely distributed across western North America. It occurs from southern British Columbia east to southwestern Manitoba and south to Minnesota, Nebraska, northern New Mexico and Arizona, and southern California [71,92]. Distributed over 53,221 mi2 (137,800 km2) of the western United States, it is 2nd only to big sagebrush in total area occupied by a sagebrush species [12,13]. Silver sagebrush is most common in the northern Great Plains, Rocky Mountain, and Intermountain regions [198]. It is relatively uncommon in the Great Basin [126]. It is rare in Utah, British Columbia, and Manitoba, and absent from Washington [38,92]. Plants database provides maps showing the overall distribution of silver sagebrush and distributions of the subspecies.

Subspecies: Bolander silver sagebrush occurs from north-central Oregon, where it occurs in montane meadows of the Ochoco and Blue mountains and on the eastern slope of the Cascade Range [37], south through mountainous regions and the eastern edge of the Great Basin to Inyo and Tulare counties, California, and east to Humboldt and Washoe counties, Nevada. Bolander silver sagebrush populations are disjunct from the other 2 subspecies [30,71,92,93,112,126].

Plains silver sagebrush occurs from southern British Columbia east to southwestern Manitoba and south to western Nebraska, eastern Colorado, central Wyoming, and south-central Montana [71,92,190]. Most common east of the Continental Divide, it is widely distributed in the northern Great Plains. Common in Saskatchewan, it becomes increasingly sparse to the south except along watercourses and bottomlands, where it may be locally abundant [90,112]. Distributions of plains and mountain silver sagebrush overlap in eastern Idaho, western Montana, across Wyoming, and in north-central Colorado. Outlying populations occur in west-central Colorado and the eastern Dakotas [71].

Mountain silver sagebrush is most common west of the Continental Divide. It is distributed from central Idaho and western Montana east to central Colorado, south to northeastern New Mexico and north-central Arizona, and west to central Nevada and eastern Oregon [71,92,112,126,190].

Physical Description

Morphology

Description

Silver sagebrush is a native shrub with semiwoody to woody stems [92]. Mature plants generally range from 1.3 to 3.3 feet (0.4-1 m) in height and are densely branched [38,168]. Plants on upland sites tend to be smaller than plants on bottomlands and other moist sites [176]. The lanceolate leaves are thin and narrow, ranging from 0.8 to 3.5 inches (2-9 cm) in length [57,157,168]. Plants with lobed leaves are probably showing introgression with big sagebrush [12,188]. Vegetative shoots are evergreen and perennial; floral shoots are annual but somewhat persistent after drying [72]. The inflorescence is a panicle of perfect disc flowers [57,75]. The fruit is a small (~ 2.5 Ã 1 mm), sticky-walled cypsela bearing a single, tiny seed [38,111,168,171,191]. Harvey [71] reported mean mass, length, and width of plains silver sagebrush seed from Montana at 680 Âµg, 2.1 mm, and 0.90 mm, respectively. The root system consists of a taproot with lateral roots [71]. Plants in Saskatchewan had deep taproots (7-10+ ft. (2-4+ m)) without much lateral branching in upper soil layers [36]. Silver sagebrush is rhizomatous; rhizomes are generally located within a few inches of the soil surface [71]. Rhizome length of plains silver sagebrush in eastern Montana averaged 3.4 feet (1.1 m): 3.3 times more than mean plant height of 13 inches (32 cm). Individual rhizomes bore 1 to 52 sprouts [187].

Plant descriptions provided in this section present information relevant to fire ecology and are not meant as identification keys. Several florae [38,57,75,111,168,191] provide keys for identifying silver sagebrush.

Subspecies: Infrataxa are morphologically distinguished by plant height and relative leaf size, color, and hairiness of herbage [75,191]. Distinctions are not clear-cut, and there is considerable overlap in the subspecies' characteristics [38]. Beetle [12] and Winward [198] provide keys for distinguishing silver sagebrush infrataxa. Gross differences in the subspecies' morphology follow.

Bolander silver sagebrush is a relatively low, thickly branched, round shrub [91]. It is less than 3 feet (0.9 m) in height. Stems are woody at the base and bear relatively small (1- to 2-inch-long (3-5 cm)), narrow leaves. Fruits are less than 1.2 mm in length, and resinous [75]. Bolander silver sagebrush is easily distinguished because of its restricted range [12].

Plains silver sagebrush is the tallest of the subspecies. It has an erect, freely branching growth form, typically reaching 3 to 4 feet (0.9-1 m) in height at maturity but sometimes as much as 4.9 to 6.6 feet (1.5-2 m) [57,90,168]. It has relatively larger, wider leaves (2-4 inches Ã 0.4 inch (4-9 Ã 1 cm)) with a denser, whiter covering of tomentum [38,89] compared to mountain silver sagebrush.

Mountain silver sagebrush is erect and freely branching in form [90]. It grows from 0.3 to 1 foot (0.1-0.3 m) in height. It is differentiated from plains silver sagebrush by its relatively shorter stature, smaller (0.8-5.3 cm long), narrower, more strongly lobed leaves, and less silvery-white (often dark green) herbage [12,85,191].

Species' stand/age class structure: Silver sagebrush communities are usually structurally simple, consisting of silver sagebrush and an understory of graminoids. Silver sagebrush is often the only shrub [65,143,155,203], and forb cover is usually sparse [64,132]. Spacing varies from widely spaced silver sagebrush plants or clustered colonies to a close arrangement of shrubs [65,69,78,132,186]. Silver sagebrush in late succession can form nearly closed cover [69,198]. Hirsch [78] found a range of 674 to 4,519 silver sagebrush per hectare in a plains silver sagebrush-western wheatgrass community in southwestern North Dakota. Another western North Dakota study showed the few forbs in the community were most abundant near plains silver sagebrush, while bunchgrasses were more plentiful in shrub interspaces [73]. Bare ground and biological soil crust cover tend to be low in undisturbed silver sagebrush communities [15,132]. On a mountain silver sagebrush community in eastern Oregon, mean bare ground and litter cover on undisturbed soils were < 3% and 80%, respectively. Maximum bare ground cover on disturbed soils was 17% [132].

Woody sagebrush species are long lived, with some species exceeding 100 years of age [193]. As a cloning species, however, silver sagebrush probably does not fit this general pattern. Maximum life span and typical age class structure of silver sagebrush need further investigation. Wambolt and others [187] found age class structure of plains silver sagebrush in eastern Montana was as follows:

Plant part

Mean age (yrs)

Standard deviation

Number of samples

stems

3.4a,1

2.0

204

taproots

6.9b

3.1

28

parent rhizome2

8.8c

3.7

68

rhizome system3

6.0b

2.5

128

1Significant (p<0.05) differences followed by different letters2Rhizome originating from a parent (or dead) stump to which sprout was directly connected.3Rhizomes sections other than in 2 above.

Drought - Drought tolerance of silver sagebrush is uncertain. The species is markedly sensitive to water stress in the seedling stage [186,187], and has been noted as either drought intolerant [112] or tolerant [47,60] at maturity. Within the species, plains, mountain, and Bolander silver sagebrush have been ranked least to most drought tolerant, respectively [163]. Anecdotal evidence from northern Great Plains studies during and after the "dust bowl" era (1937-1943) suggests that silver sagebrush is well adapted to survive severe, prolonged drought. On study sites across the northern Great Plains, adult postdrought survivorship of silver sagebrush was comparable to big sagebrush, and silver sagebrush showed better seedling establishment than big sagebrush after the drought had ended [47,144].

Ecology

Habitat

Key Plant Community Associations

Composition of silver sagebrush communities is variable across the species' broad geographical range. The communities are often compositionally and structurally simple, but are sometimes diverse, especially in riparian zones [67,78,127,177,198]. Brief descriptions of common codominants and associates are presented below by subspecies. More detailed descriptions of silver sagebrush-dominated plant communities are available in the publications listed at the end of this section.

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Habitat characteristics

Silver sagebrush requires more moisture than most sagebrush species, growing in areas that receive > 10 inches (250 mm) mean annual precipitation and have a water table within 3 feet (1 m) of the soil surface [157,176]. For example, a Bolander silver sagebrush/Sandberg bluegrass community in Plumas County, California, occurred on streamside soils with a mean July moisture content of 36% and a mean water table depth of 47.6 inches (121 cm) [173]. Because it requires moist soils, silver sagebrush typically grows on the edges of streambanks and drainages and on floodplains, bottomlands, and moist meadows [57,157,190,190].

Soils: Silver sagebrush occupies moister, colder soils than any other woody sagebrush species in North America [193]. Soil drainage is often slow. Silver sagebrush communities are also common on transitional wet-to-dryland sites [63,109] where soils dry by late summer. A mountain silver sagebrush/tufted hairgrass community in Yellowstone National Park was described as "the driest wetland community type" within the Park [24]. Phosphorus, potassium, nitrogen, organic matter, and cation exchange capacity are often lower in silver sagebrush soils than in soils of surrounding communities. Silver sagebrush cannot tolerate strongly saline or calcareous soils [73,157,185]. Soil pH ranges from slightly acidic to strongly alkaline (6.0-8.5) [24,63,66,176]. Parent materials of soils supporting silver sagebrush include sandstones, shales, and granites [130]; soil textures include clay, silt, loam, sand, and gravel [71,85,187]. Silver sagebrush in Wyoming occurred on shallow to deep soil profiles, being most common (9/14 sites) in deep soils (depths of > 3 feet (1 m)) [176]. Best growth occurs on well-drained, coarse-textured, alluvial soils that are moist in the upper 6 inches (20 cm) of the soil profile [63,185].

Subspecies: Bolander silver sagebrush is most common on pluvial lakebeds, internally drained basins with alkaline soils, and in snow catchments with granitic soils [71,91,113,163,203]. It also grows on meadows, streambanks, and moist, gravelly soils [17,75,98]. It is the only sagebrush in North America that can tolerate temporary inundation [182]. Bolander silver sagebrush occurs from 4,400 to 11,000 feet (1,300-3,400 m) elevation [17,75,98]. In the Ochoco Mountains, it occurs on the margins of mid-elevation meadows (4,400-5,600 ft. (1,300-1,700 m)) and on lower-elevation, inactive floodplains [98]. It occurs from 5,000 to 9,600 feet (1,500-2,900 m) elevation in Nevada [93].

Plains silver sagebrush occurs on low hillsides, riparian zones, and in valleys. Ranging from 4,000 to 7,000 feet (1,000-2,000 m) elevation, it is most common below 5,000 feet (1,550 m) on moist, sandy soil bordering prairie creeks, ephemeral water courses, and the bottoms of eroded hills [14,71,90,117,168]. Topography is usually flat to gently sloping [127]. Scattered plants may occur on upland sites [14].

Mountain silver sagebrush is most common on mountain meadows, stream terraces, basins, and areas of heavy winter snowpack throughout its distribution. It is occasionally found on moist upland slopes [12,85,113,191]. In the Southwest it is most common in the mountains but also occurs on plains and in valleys [111]. Mountain silver sagebrush is common on limestone-derived soils [163]. It occurs from 6,000 to 10,000 feet (2,100-3,050 m) elevation across its range [17,71,191]. Ranges for mountain silver sagebrush by state are:

A variety of fire treatments may be needed to mimic historic FIRE REGIMES. Because the fire regime of the northern Great Plains was highly variable, Sieg [165] recommends varying fire intensities and seasons, including use of mid-summer fire, to restore natural disturbance patterns. Howe [87] stated "the strategy should avoid a uniformity of timing of burns or in intervals between burns that artificially simplifies what was probably a more complex system."

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Broad-scale Impacts of Plant Response to Fire

A late summer wildfire promoted plains silver sagebrush on an Alberta western wheatgrass-blue grama prairie. The grassland, used as a cattle range, was in excellent condition prior to the wildfire. Three successive years of drought followed the wildfire, and cattle were allowed free access to burned and unburned portions of the range. Stocking rate was 0.64 AUM/ha. Plains silver sagebrush was the most common shrub in the postfire plant community, and its biomass was greater on burned than on unburned plots on both upland and bottomland sites [48].

Fire also favored silver sagebrush on the Grand Mesa National Forest,Colorado. A Gambel oak/common snowberry-Saskatoon serviceberry community (Quercus gambelii/Symphoricarpos albus-Amelanchier alnifolia) wasprescribed burned, sprayed, and/or chained to reduce density and height of big game and cattle browse. Production of silver sagebrush (kg/ha) beforeand after treatments is given below [102].

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Plant Response to Fire

Silver sagebrush has the strongest sprouting response of any woody sagebrush species in North America [25,199]. It sprouts from the root crown [134], rhizomes [12,14,17,114,187], and roots [12,14,17,114] after top-kill by fire [25,198,200]. Because of its strong postfire sprouting response, fire on a 5 to 20-year rotation promotes silver sagebrush [17,187]. It can return to or exceed canopy coverage in 4 to 6 postfire years [198]. For example, fall prescribed burning of a Bolander silver sagebrush/Baltic rush wet meadow in Inyo National Forest, California, produced no significant change in postfire silver sagebrush cover (measured for 4 postfire years) compared to prefire cover [70]. Dry weather and fuel conditions before fire can reduce the number of sprouts silver sagebrush produces after fire [195]. Very frequent fire tends to favor associated bunchgrasses over silver sagebrush [98].

Silver sagebrush requires an open, disturbed seedbed [71,147], and fire may prepare a favorable site for seedling establishment. In eastern Montana, plains silver sagebrush seedling establishment has been documented on sites disturbed by fire or ice scouring. Rhizome sprouting was more common, however (approximately 1 seedling per 3 sprouts) [187]. In a rehabilitation study using artificial regeneration, mixed sagebrush steppe in Wyoming was treated to control invading Utah juniper (Juniperus osteosperma). Control methods included herbicide (picloram) application, bulldozing, tree harvest, and a fortuitous wildfire. After the treatments and the wildfire, native species including silver, big, and black (Artemisia nova) sagebrush were seeded in, with time of seeding (spring vs. fall) and seeding method (furrow vs. broadcast seeding) evaluated. All sagebrush species established best on burned plots compared to unburned plots; fall planting and broadcasting also favored the sagebrushes compared to spring seeding and furrowing [53].

Hybrids: Silver sagebrush hybrids may inherit the ability to sprout after fire and other top-killing events. Silver sagebrush Ã mountain big sagebrush and silver sagebrush Ã threetip sagebrush hybrids both sprout after fire [97,112]. Inadequately studied, postfire sprouting response of silver Ã threetip sagebrush hybrids is probably strong because each parent has genetic ability to sprout. Silver and threetip sagebrushes were once assumed to be closely related due to common sprouting ability [12,164]; however, DNA-based phylogenetic studies show a close genetic relationship among black sagebrush, low sagebrush, and silver sagebrush infrataxa (the silver sagebrush lineage) [96,97,120], and a more distant genetic relationship between the silver sagebrush lineage and the big sagebrush lineage (which includes threetip sagebrush and big sagebrush infrataxa) [96,97]. Studies on the sprouting ability of silver, black, and low sagebrush combinations are lacking, but such studies might provide insight into the genetic basis for sprouting in woody sagebrushes and ultimately, produce woody sagebrush plants that can survive on sites where exotic annual grasses have altered FIRE REGIMES. Sprouting, drought-tolerant sagebrush hybrids may be useful in rehabilitating sagebrush rangelands that have converted to annual grasslands dominated by cheatgrass or medusahead (Taeniatherum caput-medusae) after repeated, short-interval fires. Big and threetip sagebrush seedlings are more drought tolerant than silver sagebrush seedlings. Crosses among silver, big, and threetip sagebrush may produce sprouting plants that can survive on dry sites prone to reburns [112]. McArthur and others [115] have produced a plains silver sagebrush Ã Wyoming big sagebrush hybrid with apparently fertile seed.

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Broad-scale Impacts of Fire

Fall burning under dry conditions may result in greater mortality compared to spring burning due to internal water stress of silver sagebrush plants [119,195]. Fire Case Studies summarizes a study on seasonal differences in fire effects on silver sagebrush.

Ground fires are rarely reported in silver sagebrush steppes; however, in Saskatchewan, Rowe [151] noted a September, lightning-ignited ground fire in a silver sagebrush/green needlegrass-blue grama-western wheatgrass association. In some spots, the fire burned into the taproots of silver sagebrush plants and killed them.

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Fire Ecology

Fire adaptations: Silver sagebrush has a strong sprouting response after top-kill by fire [25,38,199,200]. Because it possesses several organs capable of regeneration, including roots and rhizomes that are protected by soil, it is not as susceptible to fire mortality as most woody sagebrush species [13,119,186,187].

Although sprouting is silver sagebrush's primary method of postfire regeneration, some seedling establishment can occur if early postfire years are favorably wet during the growing season [187]. Time required for postfire sprouts to begin seed production is undocumented, but given silver sagebrush's rapid rate of sprout growth [152], sprouting stems probably fruit and seed within 2 or 3 postfire years. Seeds produced from postfire sprouts are the most likely sources of seedling establishment, but wind, water, and animal transport of seed onto burns may also contribute to postfire seedling establishment [12,49,71,159,187].

Fuels: Occupying bottomlands and other areas that are wetter than surrounding vegetation, silver sagebrush communities often have heavier litter and vertical fuel loads than surrounding plant communities [132,177,186]. Fires tend to carry into and spread in silver sagebrush unless the community has been overgrazed [17,186]. Heavy litter build-up tends to decrease rhizomatous sprouting in silver sagebrush colonies, while removal of the litter by fire or other means encourages silver sagebrush sprouting and colonial expansion [185,187].

Bolander silver sagebrush: As of this writing (2002), there are no published fire history studies on Bolander silver sagebrush communities. Bolander silver sagebrush grows on sites with widely varying characteristics, including fuel loads. Fire was probably rare in Bolander silver sagebrush communities on alkali sinks in the rain shadow of the Sierra Nevada, and frequent on Bolander silver sagebrush meadows of the Ochoco and Blue mountains. Since even plant community composition, structure, and production are poorly described in the literature, a great deal of research is needed to understand fire effects and historic FIRE REGIMES for Bolander silver sagebrush communities. Fire and rangeland managers with experience in this type are encouraged to share their findings with Fire Effects Information System staff.

Plains silver sagebrush: Fire history studies of plains silver sagebrush-grama-needlegrass steppes of the northern Great Plains are based on historic records and tree fire scars obtained from adjacent, coniferous communities and a few lone, on-site conifers. These studies suggest that stand-replacement fires occurred frequently in plains silver sagebrush steppes. Wright and Bailey [199] estimated fire frequencies of 5 to 10 years on rolling-to-level topography, where plains silver sagebrush mostly occurs as widely scattered plants in a landscape dominated by mixed grasses [71]. On topography dissected with breaks and rivers, where silver sagebrush is most common, they estimated fire return intervals of 20 to 30 years. Other researchers report similar fire return intervals for plains grassland steppes [27,52,192]. For example, fire return intervals range from 16 to 47+ years in relict western wheatgrass-green needlegrass-plains silver sagebrush communities of western North Dakota [137].

Most plains grassland fires historically occurred in summer or fall, with lightning and human ignition sources. Lightning-caused ignitions were most common in July and August. Sieg [165] suggests that for the northern Great Plains, the natural fire regime of low draws that were vegetated with sprouting species such as silver sagebrush was mostly late-growing-season fire, ignited after fine fuels had cured and dried. Late-season fires were probably "intense," but because natural fires also occurred in other seasons, the overall fire regime was highly variable. Native Americans traditionally set fires throughout the year, although April, September, and October were their peak ignition times [76].

The following table provides some fire regime intervals for plant communities and ecosystems where silver sagebrush is a dominant or important component of the vegetation. For further information on these FIRE REGIMES, see the FEIS species summaries on the community and ecosystem dominants listed below.

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Successional Status

Silver sagebrush occurs in early to late stages of succession [12,94,131,148]. Reed [143] reported mountain silver sagebrush invading abandoned hayfields in the Jackson Hole Wildlife Park of Wyoming. These silver sagebrush steppes were sometimes stable, and sometimes succeeded to quaking aspen. Silver sagebrush prefers open sites, and is intolerant of all but light shade [189]. It grows on newly exposed soils and can survive fire, browsing, and short periods of flooding disturbance [63,99]. Researchers in Montana have documented a riparian sere on the Yellowstone River that begins on bare, disturbed sandbars, progresses through development of plains cottonwood/sandbar willow (Salix exigua) gallery to a Wood's rose-western snowberry (Rosa woodsii-Symphoricarpos occidentalis) shrubland stage as trees age and die out, and climaxes in a plains silver sagebrush-western wheatgrass-prairie sandreed steppe [18,19,67]. Hansen and others [67] suggest this riverside plains silver sagebrush steppe may be a zootic disclimax induced by cattle overbrowsing the riparian zone. Nelson [127] noted a different successional trajectory in the Badlands of North Dakota. There was no evidence of shrubland and climax steppe vegetation phases after tree death; instead, plains silver sagebrush invaded open plains cottonwood (Populus deltoides ssp. monilifera) galleries, sometimes dominating the understory.

Regeneration Processes

Silver sagebrush reproduces from seed and by sprouting and layering [71,186].

Breeding system: Silver sagebrush's perfect flowers are uniformly fertile [111]. Most breeding is accomplished by outcrossing, although some selfing occurs [112]. DNA studies of plains silver sagebrush showed evidence of interpopulation outcrossing, but differences in genetic diversity among populations were not great. McArthur and others [115] state that large population sizes and wind-effected pollination tend to minimize between-population differences in silver sagebrush.

Seed production: Sagebrush species tend to have high fruit set, seed set, and germination rates. High seed production and germination rates help offset the genus' generally low rate of seedling establishment (see Seedling establishment) [182]. Although a good fruit and seed producer, silver sagebrush has a lower rate of seed production than other species in its subgenus, with fruit set 18% lower than big sagebrush [71,179]. Silver sagebrush 1st starts producing seed at about 4 years of age [147].

Seed dispersal: At time of dispersal, the involucral bracts spread and release the ripe fruits [168]. The single seed remains contained within the fruit, which falls beneath or slightly downwind of the parent plant. Some long-distance dispersal probably occurs when the sticky fruits adhere to passing animals [71,159]. Wind and water also disperse seed away from the parent plant [12,49,187]. Fruits that fall on crusted snow may be moved long distances by wind. Sagebrush seeds float, and water currents may also carry seeds considerable distances [159].

Seed banking: Studies on potential seed banking of silver sagebrush are sparse, but a few studies suggest that silver sagebrush may build up a short-term seed bank. Silver sagebrush seed retains its ability to geminate when stored under cool, dry conditions, but looses germinative capacity rapidly when exposed to unfavorable conditions. Eddleman [45] obtained better (73%) and faster germination from stratified, year-old seed than from unstratified 2-month-old seed (26% germination) in the laboratory. However, Romo and Young [148] found plains silver sagebrush seed rapidly lost its ability to germinate when exposed to field environments in Saskatchewan. Spring-sown seed showed significantly better emergence than fall-sown seed, which was more likely to be killed by fungi or drastic fluctuations in temperature. Some seeds that failed to germinate within the 1st year were still viable, and the authors suggest that silver sagebrush may have a small soil seed bank reserve on safe sites. Further studies are needed to determine ability of silver sagebrush to establish from soil-stored seed.

Germination: Silver sagebrush seed is immediately germinable, although best germination occurs when seeds are retained on the parent plant long enough to experience cold temperatures [45,186]. Seed germinates with or without light [184,186] over a wide range of temperatures [186]. Plains silver sagebrush seed collected in Montana, stored at room temperature for 2 years, and sown in the greenhouse showed 51% and 64% germination on filter paper (without and with fungicide treatment, respectively). Optimum germination appears to occur with persistently cool soil temperatures. When sown in the greenhouse, seeds showed 93% germination at 68 oFahrenheit (20 oC) and 97% germination at 59 oFahrenheit (15 oC) [71]. A Saskatchewan study found best germination of plains silver sagebrush occurred with stratification (> 28 days' duration) around 50 oFahrenheit (10 oC). Temperature range for germination was 41-77 oFahrenheit (5-25 oC) [146]. In the Montana study, exposure to relatively high temperatures (86 oFahrenheit (30 oC) for 14 days) prior to planting resulted in loss of seed viability. Germination rates were best for seed planted 2.5 mm below the soil surface. No germination occurred in seed more than 7.5 mm below the soil surface. Seeds sown on the soil surface germinated readily but were highly susceptible to desiccation [71].

Seedling establishment/growth: Although silver sagebrush seed production is high, few plants survive the germination and seedling stages [185]. Artificial plains silver sagebrush regeneration, established in southern Montana by seeding-in, showed mean 1st-year survivorship of 3.4% [71]. Seedlings require open ground that is free from competition [71,147], and they are rare in undisturbed to lightly disturbed, mature stands [71,73]. On undisturbed steppes in the Badlands of North Dakota, plains silver sagebrush comprised 100% of total shrub cover, only 4% of which was seedlings [186]. Good establishment occurs on soils disturbed by animal burrowing or tilling [147]; the incidence of postfire seedling establishment needs further study. Silver sagebrush seedling mortality is greatest in the 1st year, tending to level out after that [71,186]. Investigators in Saskatchewan [83] found that up to a critical mass, seedling establishment and growth rates of plains silver sagebrush seedlings increased with increasing weight of their originating seeds; however, plants from seeds weighting > 0.57 mg showed poor germination, and growth of seedlings from the heaviest seeds was slow. In a Saskatchewan study, Romo and Grilz [147] found that only 5-6% of sown silver sagebrush seed produced seedlings, but 85% of seedlings that survived their 1st year also survived their 2nd. Drought is the primary cause of seedling death. Seedlings require moist soil for establishment and growth [186,187], and pulses of seedling establishment have been noted in years of above-average precipitation [187].

Acclimated seedlings are cold-hardy. Plains silver sagebrush seedlings from Saskatchewan survived exposure to -38 oFahrenheit (-39 oC) temperatures after hardening-off, while nonacclimated seedlings did not survive exposure to 7 oFahrenheit (-14 oC) temperatures. The researchers suggested that seedlings germinating early in spring may show better winter survivorship than later-germinating seedlings, as older seedlings that have gradually acclimated to cooling temperatures have had more time to develop protection from freezing by lignifying cell walls and expanding twig buds [82].

Asexual regeneration: Cloning is silver sagebrush's most common method of reproduction [148,187]. With 3 methods of sprouting and the ability to layer [12,71,72,90,189], silver sagebrush is the strongest sprouter in its subgenus [71,186,200]. It sprouts from the roots [12,14,17,38,71,72,114,126], rhizomes [12,17,114,126,157,171,189], and the root crown [47,152,189] after disturbance damages stem tissue [38,72,126,157] and removes apical dominance. A strong sprouting response from buried organs increases silver sagebrush's ability to survive flood, ice scour, drought, and even severe fire damage [47,186,187]. Enlargement of colonies via sprouting and layering is nearly the sole method of silver sagebrush regeneration in the absence of disturbance; both seedlings and sprouts may occur on disturbed sites. Origin of excavated plains silver sagebrush plants in Montana was approximately 37% from seed (no connecting rhizomes) and 63% from sprouts (plants connected by rhizomes). An excavated colony consisted of 15 individuals, all connected by a rhizome running within 2 inches (5 cm) of the soil surface. Each plant had its own root system. Soil texture may affect ability to clone: the only sites where plants established from seed outnumbered those originating from rhizomes were those with very gravelly or very clayey soils [71]. Similarly, another Montana study of plains silver sagebrush regeneration found plants started from seed outnumbered cloned plants only on sites with clay pans underlaid with gravel. Typical rates of establishment were 1/3rd from seed and 2/3rds from cloning [187].

Harvey [71] found layering was an important means of regeneration for silver sagebrush in eroded gullies. Stems that had been buried in silt by periodic floods were producing adventitious roots and sprouting; rhizomes were also producing sprouts.

Sprouting from the root crown is less frequently reported in the literature than sprouting from roots or rhizomes, but root crown sprouting may be an important adaptive response to drought and browsing. Approximately 3/5ths of the plains silver sagebrush plants on an eastern Montana site gradually died back to the root crown during the severe drought of the early1930s, sprouting back from the root crown in the spring of 1935. The remaining 2/5ths did not recover [47]. In a study of the response of native shrubs to pruning (a surrogate for browsing), silver sagebrush responded to annual pruning to a height of 0.5 foot (0.2 m ) by "vigorous" sprouting from the root crown. The sprouts grew quickly: after 3 years of treatment, there was no difference in mean height between pruned and unpruned silver sagebrush plants (3 feet (0.9 m)), although crown area was significantly less in pruned vs. unpruned plants (03.2 vs. 42.4 ft2 (2.81 vs. 3.91 m2), respectively; p = 0.05). [152].

Hybrids: Silver sagebrush hybrids may inherit ability to sprout and layer [71,115]. For example, a natural mountain silver sagebrush Ã mountain big sagebrush hybrid from Gallatin County, Montana, produced root sprouts in the field and layered when moved to the greenhouse [71].

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Life History and Behavior

Cyclicity

Phenology

Although classified as evergreen, silver sagebrush sheds many of its leaves in winter [75], retaining a few until spring regrowth [168]. Leaves may drop early in response to drought [47]. Seedlings emerge and new growth of older plants starts from March to June, depending upon latitude and elevation [12,71,82,147]. In southern Montana, established plants initiate growth in late March, with seedlings emerging from mid-April to mid-June [71]. Flowering occurs in July and August in California and Oregon [72,75], from July through September in New Mexico [111], and in August and September in the Great Basin, northern Great Plains, and the interior Pacific Northwest [38,45,57,93,119,126]. The tomentum tends to thin around flowering time [38]. Seed dispersal is prolonged from early fall through the following spring [148]. Fruit and seed disperse as a unit, with most seed shattering from September through November [12,45,57,119,148,186]. Some fruits are retained on the parent plant until winter or spring [148].

Phenology of plains silver sagebrush on 6 sites across southern Montana was as follows [71]:

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Relevance to Humans and Ecosystems

Benefits

Other uses and values

Native Americans of the northern Rocky Mountains used a decoction of silver sagebrush leaves as a general tonic, and chewed the leaves to quench thirst. Blackfoot and Lakota used silver sagebrush as winter horse browse, and considered it the best sagebrush browse available for big game species. Tribes of the Great Basin used silver sagebrush branches as a fuelbed for roasting pinyon (Cembra) pinecones [123]. Many tribes use the branches in ceremonial rites [56].

Silver sagebrush is listed as a heat and drought tolerant plant suitable for xeriscaping [60]. Since young plants are not drought tolerant [186,187], generous dry-season irrigation is probably warranted for their 1st few years until plants establish a deep root system.

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Value for rehabilitation of disturbed sites

Silver sagebrush has potential as a soil stabilizer and for use in rangeland, wildlife, and riparian restoration projects [63,112,136,148,159,198]. It is established from seed, containerized stock, and nursery-grown cuttings [136,147]. Due to the species' strong tendency to layer, stem cuttings root easily [71]. Transplants have shown good growth on favorably moist sites. Plains silver sagebrush cuttings, used as part of an upland game bird habitat improvement project on the Snake River Plain of southern Idaho, showed 95% survival and good growth 5 years after transplanting [160]. Silver sagebrush also regenerates when seeded on moist sites, and is recommended for inclusion in range seeding mixtures. Seeding-in is not recommended on dry sites [41,136,198]; however, silver sagebrush seed can germinate on soils with low water potentials due to dissolved salts [45]. Spring sowing is recommended [147,148]. The seed is commercially available [138].

Rehabilitation projects show variability in silver sagebrush's ability to establish on coal mine spoils. In southern Montana, silver sagebrush sown on coal mine spoils showed poor survivorship and seedling growth compared to germinants on unmined plots [71]. However, silver sagebrush cuttings transplanted on coal mine sites in Wyoming and Colorado showed good to excellent survivorship in their 1st year. Transplants on 2 Wyoming sites treated with topsoil showed 100% survivorship. In Colorado, transplants showed 50% survivorship on sites treated with topsoil and 100% survivorship on untreated coal mine spoils. Neither the Wyoming nor the Colorado coal mine sites were irrigated after transplanting [86]. Poor results on some sites may be due to toxic soil contaminants and/or dry soils. Further information is needed on ability of silver sagebrush to establish on contaminated soils.

Information on seed collection, processing, storage, and planting is available for silver sagebrush [45,147,159,189].

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Importance to Livestock and Wildlife

Silver sagebrush provides valuable habitat and forage for wildlife. Deer, elk, pronghorn, bighorn sheep, and sage-grouse browse the foliage [51,198]. Voles (Microtus spp.) feed on silver sagebrush roots and rhizomes [186]. On the Great Plains, browsing ungulatesgenerally make little use of silver sagebrush foliage in summer [14], but use plains silver sagebrush habitats all year due to their relatively mesic conditions. Bison and mule deer, for example, make heavy year-round use of use of plains silver sagebrush/western wheatgrass steppes of Theodore Roosevelt National Park, North Dakota [65]. Mule deer may browse silver sagebrush heavily when other forage is dormant [103,108]. Silver sagebrush is also important on fall and winter ranges [89,171,186]. Bolander silver sagebrush/bottlebrush squirreltail (Elymus elymoides) communities were rated as highest-use areas for mule deer on the Silver Lake-Fort Rock winter range of Lake County, Oregon, from November through May [106]. On the Missouri River Breaks of Montana, Rocky Mountain mule deer made greatest use of silver sagebrush in winter; it was a minor component of their spring and fall diets. Silver sagebrush on the Missouri River Breaks composed 33% total volume of elk rumens (n=12) from fall samples; however, it was only present in trace amounts in samples from a preceding year. It was not found in rumen samples from cattle [108].

In regions with dry summers, livestock and wildlife may browse silver sagebrush when upland vegetation has already dried. In Modoc County of northeastern California, Bolander silver sagebrush communities were preferred summer-use areas for pronghorn, feral horses, and cattle [153]. Although a common staple for wildlife, livestock use of silver sagebrush is variable depending upon availability of palatable herbs [186]. Domestic sheep generally browse silver sagebrush more heavily than cattle [14]. Cattle may prefer grazing in silver sagebrush steppes, however, because their relatively mesic soils promotes heavier grass cover than in adjacent communities, especially in summer [95]. Livestock may actually make greater use of silver sagebrush when there is ample grass to go with it [198].

Silver sagebrush steppes are important habitat for wildlife. For example, they are the 2nd-most used habitat for sharp-tailed grouse in eastern Montana; the birds used only upland western wheatgrass-blue grama grassland habitats more than plains silver sagebrush steppes [174]. Silver sagebrush communities also provide important corridors for wildlife traveling from riparian zones to forested or grassland communities [129,132]. Three wildlife species, pronghorn, sage-grouse, and a native grasshopper, sometimes rely on silver sagebrush steppes as their primary habitat, and on silver sagebrush browse as their primary forage.

Silver sagebrush is used as an indicator species in pronghorn habitat suitability index models [3]. It provides winter maintenance and emergency forage [59,172]. Pronghorn also use silver sagebrush in the fall, particularly when vegetation on less mesic sites has dried [4,11,43]. For example, stomach samples of pronghorn taken during hunting season (Sept.-Oct.) in southeastern Montana were primarily sagebrush (plains silver and big sagebrush); several samples contained no other forage [34]. Pronghorn in Saskatchewan were concentrated on fall rangelands where plains silver sagebrush and creeping juniper (Juniperus horizontalis) were available [43]. Heavy livestock grazing can degrade silver sagebrush habitat conditions for pronghorn [66]. Fires that top-kill large patches of silver sagebrush can adversely affect pronghorn habitat [9] until sprouts have attained a few years' growth.

When plentiful, silver sagebrush is important in the diet of sage-grouse [105,140]. Where it is the primary sagebrush cover, silver sagebrush communities are critical sage-grouse habitat [1]. Crop analysis of adult sage-grouse in White Pine County, Nevada, showed the birds were consuming almost nothing but mountain silver sagebrush [59]. Sage-grouse populations at the northern and eastern boundaries of the bird's distribution are most likely to be ecologically dependant on silver sagebrush [23]. Sage-grouse in southeastern Alberta -- where other woody sagebrush taxa are uncommon -- nest under plains silver sagebrush almost exclusively, and silver sagebrush is their primary diet item [1].

Silver or sand sagebrush are the primary diet items of the sagebrush grasshopper (Melanoplus bowditchi). A North Dakota study showed crop contents of sagebrush grasshoppers were 97% silver sagebrush. High densities of sagebrush grasshoppers have never been recorded, suggesting few economic impacts and little damage to silver sagebrush populations are caused by the insect. However, little is known of the ecology and life history of sagebrush grasshopper, and further studies are needed to assess the ecological and economic impacts of the grasshopper [135].

Palatability: Silver sagebrush is 1 of the more palatable and nutritious sagebrush species [181,198]. With a mean of 11%, winter (Jan.-March) crude protein content of Bolander silver sagebrush on the Fort Rock-Silver Lake winter mule deer range in central Oregon exceeded that of either low or big sagebrush [181]. Mule deer, fed 7 sagebrush taxa collected from the Silver Lake Range in fall and winter, showed highest relative preference* for Bolander silver, low, and mountain big sagebrush in both fall and winter feeding trials. Domestic sheep showed moderate preference (browsed but did not prefer) for Bolander silver and mountain big sagebrush in fall, and showed highest preference for Bolander silver, low, and mountain big sagebrush in winter. Area of collection did not affect the animals' choices, while taxa consistently did [161].*relative preference index=% of diet/% composition available

Walton [186] has ranked Bolander, mountain, and plains silver sagebrush as most to least palatable, respectively.

Nutritional value: Nutritional content of silver sagebrush is greatest in the spring and declines slowly over winter. Silver sagebrush is rated "fair" in energy value and "fair to good" in protein value [44]. Mean chemical composition of plains silver sagebrush on the Little Missouri National Grasslands, North Dakota, was as follows [51].

Ca*

Mg*

K*

Cu*

Fe (ppm)

Mn (ppm)

Zn (ppm)

Jan.

0.36

0.20

0.82

7.7

210

36

13

Feb.

0.46

0.61

1.87

4.7

290

33

12

March

0.46

0.17

0.81

4.7

223

39

14

April

0.56

0.29

1.78

5.9

233

72

21

May

0.84

0.57

2.90

6.3

437

119

18

June

0.79

0.47

1.33

5.4

212

46

19

July

1.02

0.45

1.25

0.8

193

39

13

Aug.

0.49

0.33

1.27

4.6

227

35

16

Sept.

0.65

0.30

0.97

3.9

207

43

12

Oct.

0.67

0.33

0.88

3.2

293

48

12

Nov.

0.58

0.31

0.86

3.7

250

47

11

Dec.

0.64

0.30

0.81

3.7

257

32

14

*Dry-weight pecentages.

Based upon nutritional content (protein, carbohydrate, fat, vitamin, and mineral ), palatability, and dependability of supply on rangelands, silver sagebrush is rated low to fair forage for cattle, fair to good for domestic sheep, and good for pronghorn, elk, and deer [63,145].

Cover value: Silver sagebrush provides thermal and hiding cover for small mammals, small nongame birds, and game birds [44,66]. At the lower end of its elevational range, it provides important sage-grouse nesting cover [198].

"On these hills many aromatic herbs are seen; resembling in taste, smel [ sic ] and appearance, the sage, hysop, wormwood, southernwood and two other herbs which are strangers to me the one resembling the camphor in taste and smell, rising to the height of 2 or 3 feet; the other about the same size, has a long narrow, smo[o]th, soft leaf of an agreeable smel [ sic ] and flavor; of this last the A[n]telope is very fond; they feed on it, and perfume the hair of their foreheads and necks with it by rubing [ sic ] against it." [12]

It generally reaches 50–150 cm in height, with examples west of the Continental Divide typically being shorter than those east of the divide.[6]

The leaves have a narrow blade shape, are evergreen, grey-green in colour, and have a distinct aroma.[6]

^Artemisia cana was first described and published in Flora Americae Septentrionalis; or, a Systematic Arrangement and Description of the Plants of North America 2: 521. 1813 "Plant Name Details for Artemisia cana". IPNI. Retrieved August 15, 2011.

Artemisia cana ssp. viscidula (Osterh.) Beetle [12,92,117] mountain silver sagebrushWithin this summary, "silver sagebrush" refers to the species as a whole.Infrataxa are referred to by the 3 common names listed above. Not all authorities

recognize infrataxa within silver sagebrush [38,190]. Hybrids: The sagebrush genus is evolving rapidly, and hybridization is an important factor in its evolution [96,97,113,116,188]. Silver sagebrush readily hybridizes with other woody sagebrush species (Artemisia subgenus Tridentatae) including threetip sagebrush (A. tripartita), big sagebrush (A. tridentata) [117,188,190,191],and low sagebrush (A. arbuscula) [12,117,190]. Silver sagebrush ÃÂ mountain big sagebrush (A. t. ssp. vaseyana) and silver sagebrush ÃÂ Lahontan sagebrush (A. a. ssp. longicaulis) hybrids form stable, self-reproducing populations that some authorities classify as distinct taxonomic entities (snowfield sagebrush (A.spiciformis Osterh.) and coaltown sagebrush (A. argilosa Beetle), respectively) [12,114,116,118,163]. Silver sagebrush infrataxa also hybridize with each other, although Bolander silver sagebrush is geographically isolated from the other 2 subspecies and does not do so naturally [12,38,114]. Sagebrush hybrids are important ecologically as well as evolutionarily, often tolerating a broader range of ecological conditions than either parent [116]. Fire effects to silver sagebrush hybrids are discussed in that section of this review.